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Level 2 Inspection: BIORETENTION NOTE: Key Source for this Information (CSN, 2013) Recommended Repairs Triggers for Level 3 Inspection Observed Condition: Severe erosion of filter bed, inlets, or around outlets Condition 1: Erosion at inlets The lining (e.g., grass, matting, stone, rock) may not be adequate for the actual flow velocities coming through the inlets. First line of defense is to try a more non-erosive lining and/or to extend the lining further down to where inlet slopes meet the Bioretention surface. If problem persists, analysis by a Qualified Erosion (rills, gullies) is more than 12 Professional is warranted. inches deep at inlets or the filter bed or more than 3 inches deep on side slopes. If the issue is not caused by moving water Condition 2: Erosion of Bioretention filter bed but some sort of subsurface defect. This may manifest as a sinkhole or linear This is often caused by “preferential flow paths” through and along the depression and be associated with Bioretention surface. The source of flow should be analyzed and methods problems with the underdrain stone or pipe employed to dissipate energy and disperse the flow (e.g., check dams, rock or underlying soil. splash pads). Condition 3: Erosion on side slopes Level 3 inspection necessary Again, the issue is likely linked with unanticipated flow paths down the side slopes (probably overland flow that concentrates as it hits the edge of the slope). For small or isolated areas, try filling, compacting, and re-establishing healthy ground cover vegetation. If the problem is more widespread, further analysis is required to determine how to redirect the flow. Observed Condition: Significant sediment accumulation, indicating an uncontrolled source of sediment Condition 1: Isolated areas of sediment accumulation, generally less than 3-inches deep More than 2 inches of accumulated Sediment source may be from a one-time or isolated event. Remove sediment cover 25% or more of the accumulated sediment and top 2 to 3 inches of Bioretention soil media; replace Bioretention surface area. with clean material. Check drainage area for any ongoing sources of sediment. “Hard pan” of thin, crusty layer covers majority of Bioretention surface area and seems to be impeding flow of water down Condition 2: Majority of the surface is caked with “hard pan” (thin layer of through the soil media. clogging material) or accumulated sediment that is 3-inches deep or more New sources of sediment seem to be accumulating with each significant rainfall This can be caused by an improper construction sequence (drainage area not event. fully stabilized prior to installation of Bioretention soil media) or another chronic source of sediment in the drainage area. Augering several holes down through the media can indicate how severe the problem is; often the damage is confined to the first several inches of soil media. Removing and replacing this top layer Level 3 inspection necessary (or to the depth where sediment incursion is seen in auger holes) can be adequate, as long as the problem does not recur. Page 3 of 4 Page 299 of 1493